216 ANATOMY OF THE CENTRAL NERVOUS SYSTEM. 



teriorly on to the mesial surface of the brain, and here runs forward some 

 distance. Its subiculum, the cortex, which is not inroUed and lies directly 

 on the base of the brain, then passes immediately over into the lobus supra- 

 callosus — gyrus fornicatus in man. 



In man the hippocampal gyrus does not extend up under the corpus callosum. 



Since the lobus supracallosus turns down anteriorly to the base of the 

 brain and appears to reach again the olfactory area with its most anterior 

 end, this entire portion of the cortex forms a kind of arch around the margin 

 of the hemisphere. Broca, who first discoyered that the various cortical 

 tracts entering it all stand in a direct relation as to size with the develop- 

 ment of the olfactory apparatus, has designated the lobus limhicus — as he 

 named the entire area — as the olfactory cortex. 



It is a question with me whether the gyrus fornicatus belongs to tlie olfactory 

 apparatus. 



The lobus limbicus is always separated from the rest of the brain by a 

 large, distinct fissure: the fissura linibica. Its upper, curved portion has 

 already been met with in man as the sulcus cinguli. According to the in- 

 vestigations of ZucJierJicmdl, the gyrus dentatus and its continuation upon 

 the upper surface of the corpus callosum, the stria of Lancisi, must also be 

 included in the lobus limbicus. All of these gyri which thus surroimd the 

 edge of the hemisphere — the lobus olfactorius, the gyrus hippocampi, and 

 the gyrus fornicatus, the stria of Lancisi and the fascia dentata — are very 

 strongly developed in animals having highly perfected olfactory organs. 

 They are somewhat atrophied in those animals which have small olfactory 

 lobes, as is the case with man. In the dolphin, which has no olfactory lobe, 

 they are developed the least of all {Broca. Zuclierl-andl). These parts of the 

 brain, belonging manifestly to the olfactory apparatus, are included with 

 the lobus olfactorius under the term rhinenceplialon, suggested by Turner. 

 The elements of the rhinencephalon, the sulci and gyri, may be demon- 

 strated in all mammals with a certain constancy of arrangement. 



The separate parts of the lobus limbicus of the right and left side are 

 connected with one another by a large commissural system: the commissura 

 anterior. Its anterior pedicle arises in the lobus olfactorius of the one side, 

 and, curved in the shape of a horseshoe, passes over at the base of the brain 

 to the lobus of the other side. A posterior pedicle unites the lobi cornuum 

 Ammonis, or at least the regions of the cortex which lie directly without the 

 in-rolling of the cornu Ammonis. Finally, an ascending branch of the an- 

 terior commissure is recognized in many mammals. It passes into the 

 capsula externa and is well adapted to connect the dorsal part of the mar- 

 ginal gyrus with parts lying opposite. 



